This invention relates to a system for conducting electrophysiology ("EP") studies on a patient's heart using an implantable cardioverter/pacer. The implantable device, after being placed in an "EP study" mode, receives pacing trigger pulses that are transmitted to the system by an external transmitter/receiver unit. These trigger pulses are provided as an input to the implantable device to control the cardiac pacing pulses applied to the heart of the patient. Electrocardiogram ("ECG") signals are simultaneously transmitted from the implantable system, in real time, to the external unit.
EP studies of the heart are frequently required to test the heart's reaction to a variety of treatments. For example, such EP studies typically require the delivery of various cardioverting and pacing pulses to the heart to determine the response of the heart to such pulses. Such information is desirable prior to surgical implants of pacers, cardioverters or defibrillators.
For example, as part of the implant procedure for automatic cardioverter/defibrillators, it is necessary to determine the energy level threshold needed to cardiovert or defibrillate the patient's heart. These patient thresholds are customarily evaluated prior to implant through implanted electrodes that extend from the heart of the patient. The procedure generally involves, first, the implantation of the cardioverter/defibrillator electrodes that are believed to be most suitable for the particular patient, second, exercising the patient by inducing an arrhythmia that is most likely to occur within the particular patient, and, third, attempting to cardiovert or defibrillate the patient to establish the desired energy level for the implanted device. The various arrhythmias can be induced by electrically stimulating the heart through the implanted electrodes by an external device. Pacing pulses are typically used to stimulate the heart from normalcy to an arrhythmia condition. Once the patient involved in the EP study is experiencing the desired fatal arrhythmia, the external unit is fired through the implanted electrodes in an attempt to convert the arrhythmia. This procedure is repeated until the physician learns which arrhythmias may reoccur in the particular patient and the threshold energy at which the patient can be brought out of the arrhythmia and return to normalcy.
One technique for conducting EP studies is through the use of an external programmable electrical stimulator which is connected with the heart tissue by wires extending through the skin of the patient to implanted electrodes. Such programmable electrical stimulator systems receive ECG information of the heart, through conventional ECG skin electrodes attached to the skin of the patient, and provide pacing pulses to the implanted electrodes for delivery to the heart. These conventional programmable stimulators may deliver pacing pulses in various standard pacing modes. The operator of the unit can select the particular pacing pulse sequence by manipulation of various dials or switches on the stimulator. A disadvantage of this technique is that an invasive procedure is necessary to implant the pacing electrodes each time an EP study is required.
EP studies are frequently desirable for persons who have already received an implantable pacer or cardioverter. Sophisticated pacers often include a non-invasive communication link whereby signals may be transmitted from outside the body to direct the pacer to emit stimulating pulses of a predetermined type or sequence which have been pre-programmed within the implantable pacer. While such systems may have utility in conducting EP studies, and overcome the disadvantage of requiring further invasive electrode implant procedures, nevertheless the EP study is limited to the particular pacing pulse sequence that had been programmed into the unit. Moreover, ECG skin electrodes, or even implanted electrodes, are still required to detect the ECG information, in real time, during the EP study.
U.S. Pat. No. 4,187,854 discloses an implantable pacing unit that is capable of both transmitting ECG information, without wires, to an external unit, and of receiving electromagnetic energy from the external unit to power the implant and to deliver pacing pulses. A disadvantage of this system is that the sole energizing source for the pacing pulses resides in the external unit. Thus, the implanted unit cannot operate independently as a pacer without the external unit. While such a system may be useful in conducting an EP study, it would appear unable to also perform as an implantable pacer having an independent implantable power source, thus lacking the versatility of the present invention.